The present invention relates to a drawing device having a magnetic coil scanning element, which is useful with optical instruments which scan an image on a drawing table, and convert the image into an electrical signal by means of an electronic evaluation means. With the aid of such a drawing device, preferably a pencil, an observer is capable of scanning a structural element on the grid plate designed drawing table and converting it into impulses which can be read on an evaluating instrument or stored.
For the determination of volumetric proportions or particle numbers, a microscope with a drawing tube is preferably used, which makes it possible to reflect the grid plate into the beam of the microscope. The observer is thus able to view the image of his object with the grid of the grid plate superimposed thereon. In addition, to the extent that it is passed over the grid plate, the drawing pencil is also recognizable.
The accuracy of these measurements is dependent on the precision with which the magnetic coil generating the impulses senses the image superimposed on the grid plate. In order to maximize the sensing ability of the magnetic coil, it is essential to bring the coil as close as possible to the writing tip. One approach to this problem has been to dispose the magnetic coil annularly around the drawing pencil in the immediate vicinity of the writing tip. With devices which do not possess a genuine drawing capability but contain only a scanning element, the foregoing problem is not encountered. There, the magnetic force field can be transmitted by a metallic pin. Such an arrangement cannot be utilized with genuine writing instruments. In such instruments, the magnetic coil must therefore be brought as close as possible to the writing tip of the instrument.
Drawing pencils with magnet coils mounted in an annular manner around the pencil suffer from the disadvantage, however, that they are only fully effective in the vertical position. In addition, with the drawing pencils known heretofore it is not possible to determine accurately whether the magnetic coil has been activated, due to the lack of any sensible or visible means of control. Moreover, with drawing pencils having an annularly mounted magnetic coil scanning element, the placement of the coil prevents complete utilization of the pencil lead. Accordingly, there exists a great need in the art for a drawing device for use with scanning apparatus which alleviates the foregoing disadvantages.